Project 1: Immunotherapy of chronic HBV and HCV infection We have continued the virological and immunological analyses of cryopreserved blood and liver biopsy samples from chimpanzees that were collected under approved protocols prior to the NIHs decision to discontinue research with live chimpanzees. At that time chimpanzees with chronic HBV and HCV infection received immunotherapy to assess whether effective immune responses can be restored. Virus-specific T cell responses are typcially weak and functionally impaired in chronic HBV and HCV infection but strong in those who clear the infection spontaneously. Specifically, two chimpanzees with chronic HBV infection had been treated with autologous T cells that were transduced with a chimeric, antibody-based receptor (CAR) to HBsAg. Two chimpanzees with chronic HCV infection had been treated with autologous T cells that were transduced with T cell receptors from chimpanzees that had successfully cleared acute HCV infection. The HCV chimpanzees also received an immunization with a candidate HCV vaccine in order to boost the T cell response. As stated above these studies with live chimpanzees were completed prior to the NIH decision to discontinue research with live chimpanzees. We have now completed the analysis of the immunological and virological results. The results show that the adoptively transferred T cells home to the liver after infusion. They rapidly become activated, but downregulate IFN-gamma production within weeks. The transferred T cells coexist at low frequency for months after infusion in the presence of unaltered viremia and do not select for viral escape mutants. The frequency of these transferred HCV-specific T cells can be boosted by vaccination with their cognate antigen, but does not result in a change in viremia. These findings may have implications for mechanisms of T cell exhaustion and immunotherapy in other diseases of chronic antigen persistence. Project 2: Regulation of immune responses to viruses In this project, we are using mouse models of lymphocytic choriomeningitis virus and influenza A virus infection to investigate mechanisms that affect immune responses in the liver and at extrahepatic sites. Specifically, we are studying whether low level pre-exposure to antigens influences the outcome of a viral infection, and we have initiated studies on the influence of bacteria in the gastrointestinal tract on the immune response. A fast growing body of literature arising over the past few years demonstrated that commensal bacteria, in particular those of the gastrointestinal tract, are indispensible not only for digestion and metabolism, but also for the development and regulation of local and systemic immune responses. Despite this knowledge about the importance of the commensals, the microbiota within the commonly used laboratory mouse strains are not standardized. Thus, we investigate the impact that defined gastrointestinal microbiota exert on the mmune system and the outcome of viral infections. The identification of beneficial host-microbe interactions and the characterization of their immunomodulatory mechanisms are necessary to understand the regulation of immune responses in health and disease.